The present invention relates to an aerodynamic profile for aircraft and wind power stations, and to a method of measuring the thickness of ice on such an aerodynamic profile.
Aerodynamic profiles, such as rotor blades of helicopters and wind power stations (and also wings of airplanes) are subject to the formation of ice on their surface. Uneven ice shapes, for example in the form of ice noses, are particularly dangerous because the air current is more likely to stall here than in the case of a uniform thick and smooth ice layer. FIG. 2 illustrates the leading edge 7 of an aerodynamic profile with a non-uniform ice layer 8 thereon, which can easily lead to a stall.
In order to counteract the general problem of the icing of aerodynamic profiles, it is necessary to be able to detect the ice layer, and to measure its thickness. However, for more extensive investigations of ice formation and to avoid safety risks, not only the thickness of the ice layer but also its shape the aerodynamic profile should be measured. For this purpose, in the past the formed ice has been sawn after a flight through the icing region, and its shape has been measured. As an alternative, there has been the possibility of mounting riders with optical markings on the wing or a rotor blade, which riders are observed by a camera in order to be able follow the process of monitoring the markings by the ice that is being added.
Various documents describe the use of ultrasound for the detection of ice on wings or aerodynamic profiles. However, the known methods are limited to detecting the ice and measuring its thickness by individual transducers. The shape of the ice on the wing is not measured.
In this context, U.S. Pat. No. 4,628,736 describes a method and apparatus for measuring the thickness of ice by means of ultrasound, in which an ultrasonic pulse is emitted by a transducer or ultrasonic generator situated on the surface in the region of the leading edge of the wing. The ultrasonic pulse extends through the ice to its surface where it is reflected and received again at the ultrasonic generator. The thickness of the ice is determined from the transit time of the pulse.
U.S. Pat. No. 5,095,754 describes a similar method of determining the thickness of ice, but the sound generator is arranged on the underside of a buffer block whose surface is arranged in the plane of the actual ice accumulation surface.
Furthermore, U.S. Pat. No. 5,507,183 shows a method and apparatus for detecting of ice on the surface of a structure, such as a wing, in which ultrasonic waves originating from an ultrasonic generator are transmitted in the direction of the surface of the wing and, after the reflection at the interfaces of the ice layer situated thereon, are received at an ultrasonic receiver.
However, the measures for detecting ice on aerodynamic profiles known so far have the disadvantage that they cannot determine the shape of the ice. Furthermore, high construction expenditures are required for installing the known measuring devices into the wings or profiles.
It is therefore an object of the present invention to permit an online measurement of the shape of the ice on aerodynamic profiles without mounting additional components which impede the flow.
This and other objects and advantages are achieved by the method and apparatus according to the invention, which comprises an aerodynamically shaped structure and a phased array controlled ultrasonic generator arrangement which is arranged within the aerodynamic profile. During operation, the ultrasonic generator emits ultrasonic waves in a targeted manner in different directions in order to determine the profile of the thickness of a ice layer on the surface of the aerodynamic profile. As a result of the invention, an online measurement of the ice profile becomes possible without mounting additional components on the rotor blade or the wing, which components impede the flow. During a flight, a profile of the ice layer on an airplane wing or on a rotor blade of a helicopter can thus be determined. In the case of wind power stations, the profile of the ice thickness on the rotor blade can be determined and observed in real time. By observing the ice profile during the flight or the operation, appropriate measures can rapidly be taken as soon as the form of the ice layer assumes a shape which may, for example, result in a stall.
The ultrasonic generator arrangement is preferably a phased array and/or comprises an array of ultrasonic generators.
The invention makes it is also possible to determine the planar ice distribution on the aerodynamic profile, in order to calibrate codes for the icing simulation. This is necessary, for example, for flight tests.
Another advantage of the invention is the fact that no sensors are arranged on the surface of the aerodynamic profile so that no disturbances or failures or damaging of the sensors can take place by abrasion, erosion, etc.
The ultrasonic generator arrangement is advantageously further developed for carrying out a scan of the ice cover. The thickness of the ice profile can therefore be determined particularly rapidly.
Preferably, the ultrasonic generator arrangement is laminated into an aerodynamically shaped structure which is made, for example, of a composite fiber material. As a result, the ultrasonic generators are particularly protected, and the construction expenditures and thereby the costs are simultaneously reduced.
As an alternative, the ultrasonic generator arrangement may also be arranged outside the region made of composite fiber material, for example, between a foam core of the aerodynamic profile and the adjoining composite fiber material or inside the foam core. This has the advantage that the ultrasonic generator arrangement can be fitted in a particularly simple manner, and no laminating-in is required. Furthermore, the fiber structure or the carbon fiber structure is not disturbed by the ultrasonic generator arrangement.
The ultrasonic generator arrangement may, for example, be in the form of a one-dimensional embodiment; That is, it may comprise a series of successively arranged ultrasonic generator elements. As a result, a scan of the deposited ice layer on the aerodynamic profile can be carried out even by means of a relatively small number of ultrasonic generator elements.
The ultrasonic generator arrangement may also be in the form of a two-dimensional embodiment; That is, it may comprise a plurality of ultrasonic generator elements which are arranged in a planar fashion or in a plane. In this manner, it becomes possible to scan a planar area of the ice layer, so that a two-dimensional profile of the deposited ice layer can be created almost in real time. This means that the profile of the thickness of the ice can be determined in two directions, and a model can thereby be prepared of the ice layer deposited on the aerodynamic profile.
The ultrasonic generator arrangement comprises, for example, a number of piezo transducer elements, which can be implemented particularly in the form of a PVDF foil or other ultrasound-emitting flexible substrates.
Furthermore, the piezo transducer elements can be arranged below an erosion protector of the aerodynamic profile. As a result the individual elements automatically emit wave fronts perpendicular to the surface of the aerodynamic profile. The piezo transducer elements are then, for example, not operated as a phased-array ultrasonic generator arrangement but are individually controlled. That is, the thickness of the ice is measured locally at each piezo transducer element, and, as a result of their planar composite action, the elements, in turn, allow the two-dimensional measurement of the ice profile.
The aerodynamic profile may be a rotor blade for a helicopter or for a wind power station, or it may be a wing of an airplane.
According to another aspect of the invention, a method of measuring the thickness of ice on an aerodynamic profile includes the steps of: Emitting ultrasonic waves to the surface of the aerodynamic profile; receiving the ultrasonic waves reflected at the interfaces of an ice layer; determining the thickness of the layer of ice by analyzing the transit time of the reflected ultrasonic waves within the ice layer or by analyzing interferences. The ultrasonic waves are transmitted in a targeted manner to various positions of the surface of the aerodynamic profile, and at least one region of the surface is scanned by means of the targeted ultrasonic waves in order to determine the profile of the thickness of the ice.
The method according to the invention essentially has the same advantages as the aerodynamic profile.
The profile of the thickness of the ice is preferably determined from the transit time of the ultrasonic waves reflected back at interface of the ice layer. If the transit time through the wing is too short compared to the time which the piezo elements require for switching between the transmitting and receiving modes, an additional layer can be inserted between the wing and the piezo element which decelerates the sound propagation. Furthermore, this layer may be implemented by means of flexible substances and, with respect to the acoustic impedance, may be adapted such that as much sound energy as possible changes over into the wing and into the ice layer. Simultaneously, the received signal can be analyzed by the interface of this deceleration layer as a reference signal in order to compensate temperature-caused effects and additional interfering effects.
The profile of the thickness of the ice can be determined by analysis of interferences of the ultrasonic waves reflected and superimposed on at least two interfaces at the ice layer.
The wave fronts of the ultrasonic waves advantageously impinge essentially perpendicularly on the surface of the aerodynamic profile.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.